CLINICAL STUDY: ULTRASOUND CORONARY IMAGING
Detection of coronary restenosis aftercoronary angioplasty by contrast-enhanced transthoracic echocardiographic Doppler assessment of coronary flow velocity reserve
Massimo Ruscazio, MD*,*,
Roberta Montisci, MD*,
Paolo Colonna, MD*,
Carlo Caiati, MD*,
Lijun Chen, MD*,
Giorgio Lai, MD*,
Mauro Cadeddu, MD*,
Raimondo Pirisi, MD* and
Sabino Iliceto, MD, FACC
* Department of Cardiovascular and Neurological Science, University of Cagliari, Italy
Division of Cardiology, Department of Internal Medicine, University of Padua, Italy
Manuscript received May 8, 2001;
revised manuscript received May 9, 2002,
accepted May 24, 2002.
* Reprint requests and correspondence: Dr. Massimo Ruscazio, S. Giovanni di Dio Hospital, via Ospedale 46, 09124, Cagliari, Italy.
ruscard{at}unica.it
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Abstract
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OBJECTIVES: This study sought to evaluate the diagnostic potential of contrast-enhanced transthoracic echocardiography (CE-TTE) during adenosine infusion, a noninvasive method for evaluating coronary flow reserve (CFR), in detecting restenosis after successful percutaneous transluminal coronary angioplasty (PTCA).
BACKGROUND: Restenosis is the most important limitation of PTCA, and CFR can be impaired in patients with angiographically documented significant coronary stenosis.
METHODS: We performed 6 ± 2 months of follow-up of 53 patients after successful elective PTCA in the left anterior descending coronary artery (LAD). Coronary angiography was performed at the end of the planned follow-up period or even before, if clinically indicated. Thus, of the 53 patients, a total of 63 angiographic studies were performed; CE-TTE assessment of CFR was achieved before each of the 63 angiographic studies.
RESULTS: Coronary angiography revealed the presence of restenosis (defined as >50% stenosis at a previous PTCA site) in 32 angiographic examinations (group A) and no coronary restenosis in the remaining 31 examinations (group B). Coronary flow reserve was significantly reduced in group A compared with group B (1.65 ± 0.5 vs. 3.17 ± 0.8, p  0.001). A noninvasive CFR value 2 was 93% specific and 78% sensitive for detecting significant restenosis, with positive and negative diagnostic accuracies of 92% and 80%, respectively.
CONCLUSIONS: Noninvasive CFR assessment by CE-TTE is an accurate method of monitoring significant restenosis in the LAD when following up patients submitted to elective PTCA.
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Abbreviations and Acronyms
| | CE-TTE | | contrast-enhanced transthoracic echocardiography | | CFR | | coronary flow reserve | | DFW | | Doppler flow wire | | LAD | | left anterior descending coronary artery | | MRI | | magnetic resonance imaging | | PTCA | | percutaneous transluminal coronary angioplasty |
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Since its clinical introduction, percutaneous transluminal coronary angioplasty (PTCA) has shown major limitations as far as the incidence of restenosis (1,2), usually occurring within the first months after the procedure (3). Although angiography is commonly considered as the "reference standard" in defining restenosis, it is inadequate in monitoring vessel anatomy and assessing the functional importance of eventual restenosis because of its invasiveness and exclusive morphologic investigation (4).
Coronary flow reserve (CFR) is impaired in the presence of significant coronary stenosis (5) and recovers after successful PTCA (6). Thus, CFR assessed with the intracoronary Doppler flow wire (DFW) is used to evaluate PTCA results (7). However, its clinical use is limited in follow-up studies because of its invasiveness and the consequent immediate CFR assessment after PTCA. Recently, noninvasive evaluation of CFR obtained by phase-contrast magnetic resonance imaging (MRI) has been proposed to identify flow-limiting stenosis in patients with clinical signs of ischemia after PTCA (8). However, MRI assessment of CFR, although noninvasive and therefore ideal for long-term monitoring, has limited clinical applicability because it is expensive and not generally available.
We have recently developed a new noninvasive technique based on contrast-enhanced transthoracic echocardiography (CE-TTE) for the assessment of CFR in the left anterior coronary descending artery (LAD) (9). Coronary flow reserve obtained by this new method correlates with coronary anatomy severity (10) and intracoronary DFW (11,12).
The aim of this study was to assess the diagnostic potential of noninvasive evaluation of CFR obtained by CE-TTE in monitoring significant restenosis in the LAD of follow-up patients submitted to elective PTCA.
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Methods
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Study group.
Fifty-three patients (35 men and 18 women; mean age 62 ± 9 years [range 30 to 80]) with coronary artery disease submitted to elective PTCA of the LAD were scheduled for an angiographic control study at an average of six months (6 ± 2 months) after PTCA (Table 1). Exclusion criteria included patients with a previous myocardial infarction in the LAD territory, grade II or III atrioventricular block, severe chronic obstructive pulmonary disease, and bronchospasm.
Follow-up protocol.
All patients underwent diagnostic coronary angiography at the end of the planned follow-up period or before, if clinically indicated (occurrence of new, typical angina and evidence of ischemia on routine noninvasive cardiac imaging tests). The day before each of the angiographic studies, noninvasive assessment of CFR was performed by means of CE-TTE. During follow-up, a new PTCA procedure, at a previous PTCA site, was performed if clinically indicated. If a new PTCA was performed, a new follow-up study was started. The study was approved by the institutional ethics committee, and all patients were informed of the purpose and nature of the study and they provided written, informed consent.
Contrast-enhanced transthoracic Doppler echocardiography.
Echocardiography was performed for CFR evaluation using CE-TTE before and after adenosine infusion, as previously described (9–11), with an ultrasound system (Sequoia C256, Acuson, Mountain View, California) connected to a broad-band transducer with second harmonic capability (3V2c). All studies were continuously recorded on 0.5-in. (1.27-cm) S-VHS videotape. Briefly, CFR was measured in the distal portion of the LAD, first obtaining a modified foreshortened two-chamber view or, if a distal LAD flow recording was not feasible, using a low parasternal short-axis view of the base of the heart, as previously described (9–11). If the angle between color flow and the Doppler beam was >20°, angle correction was performed using the software package included in the software unit. Administration of the contrast agent (Levovist, Schering AG, Berlin, Germany) (13) was performed both before and during adenosine intravenous administration. The echocardiographic contrast agent was administered by infusion, using a devoted infusion pump (IVAC P4000 anesthesia syringe pump, Medical System, Hampshire, UK) with a concentration of 300 mg/ml and an infusion rate ranging from 0.5 to 2.0 ml/min, according to the quality and entity of the Doppler signal enhancement achieved.
Coronary flow velocity reserve assessment.
All patients had Doppler recordings of the LAD with adenosine infusion at a rate of 0.14 mg/kg per min for 5 min. All patients had continuous heart rate and electrocardiographic monitoring, as well as blood pressure recording at baseline, during adenosine infusion, and at recovery. Cardiac medications were interrupted before adenosine, although all medications or methylxanthine-containing substances were withheld 48 h before the study. Beverages containing methylxanthine substances (e.g., coke, tea, coffee) were restricted for 24 h before the study. Coronary flow reserve in the LAD was calculated by one experienced echocardiographer (Dr. Montisci) performing the test, with no knowledge of the angiographic and clinical data, as the ratio of hyperemic to basal diastolic flow velocity (for each variable, the highest of three cycles was averaged) (10). Patients studied were unselected, including those with a large body mass.
Observer variabilities.
Interobserver and intraobserver variabilities in assessing CFR have been previously assessed in our laboratory (9); they were 3.2% and 3.0%, respectively.
Coronary angiography.
Coronary angiography was performed using the standard Judkins’ method with the femoral or radial artery approach, as indicated. Coronary stenosis was assessed using orthogonal angiographic projections by one investigator who was unaware of the CE-TTE results (Dr. Ruscazio). Quantitative angiographic analyses were performed with a computer-assisted analysis system (Medcon Ltd., Tel Aviv, Israel) or with an automatic system for biplane quantitative coronary arteriography from 35-mm films (14). Coronary restenosis in the LAD was defined as >50% lumen diameter narrowing at a previous PTCA site on the follow-up angiogram.
Statistical analysis.
Continuous variables are expressed as the mean value ± SD. Differences in the absolute value and in the percent increase in velocity were assessed by the paired or unpaired t test, as appropriate. Sensitivity and specificity were calculated in the usual manner.
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Results
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A total of 63 angiographic studies were performed in the group of 53 patients considered in this study. Of these 63 angiographic studies, only 16 were performed before the initially scheduled time, because they were clinically indicated, whereas the other 47 were obtained at the established end of follow-up (6 ± 2 months after PTCA). Coronary angiography revealed significant restenosis (lumen narrowing >50%) in 32 angiographic examinations (group A) and no coronary restenosis in the remaining 31 examinations (group B).
Evaluation of CFR.
Pulsed-wave Doppler tracings suitable for CFR evaluation were obtained in 50 patients in the distal portion of the LAD and in the remaining 3 patients in the mid portion of the vessel. In all patients, CE-TTE studies were well tolerated. Figures 1 and 2 show two different clinical cases, both correctly identified by CE-TTE. In the first patient, coronary angiography six months after PTCA showed the absence of restenosis; in the second patient, coronary angiography performed five months after PTCA, before the end of follow-up, because of angina reoccurrence, showed the presence of coronary restenosis at a previous PTCA site.
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Figure 1 Absence of left anterior descending coronary artery (LAD) restenosis after percutaneous transluminal coronary angioplasty (PTCA) at six-month follow-up angiography in Patient no. 8 (see Table 1). Severe LAD stenosis (upper left panel) was successfully treated with PTCA and stent placement (upper middle panel). At the end of follow-up, angiography showed the absence of restenosis (upper right panel). Coronary flow velocity assessed by contrast-enhanced transthoracic echocardiography on the day before angiography increased from baseline (lower left panel) to post-adenosine administration (lower right panel), with a calculated coronary flow reserve of 3.6. The arrows indicate the PTCA site. CX = circumflex artery.
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Figure 2 Restenosis in the LAD five months after PTCA in Patient no. 27 (see Table 1). In the upper left panel, tight coronary stenosis (arrow) was successfully treated by PTCA and stent placement (upper middle panel). Coronary angiography performed at five months, before the scheduled end of follow-up, because of angina recurrence, revealed 72% intrastent stenosis of the proximal LAD (upper right panel). Coronary flow velocity assessed by CE-TTE on the day before angiography did not increase from baseline (lower left panel) to post-adenosine administration (lower right panel), showing severe impairment with a calculated CFR value of 1.1. The arrows indicate the PTCA site. See Figure 1 for abbreviations.
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In the basal state, peak diastolic velocity in the LAD was not significantly different between group A (37 ± 12.6 cm/s) and group B (33 ± 13.7 cm/s). However, CFR, as shown in Figure 3, was significantly impaired in group A compared with group B (1.65 ± 0.5 vs. 3.17 ± 0.8, p 0.001). Severe impairment of CFR (2) was found in most patients in group A (25/32 [78%]), but in only two patients in group B (2/31 [6%], p < 0.001). Sensitivity, specificity, and positive and negative diagnostic accuracies of noninvasive assessment of CFR in detecting coronary restenosis were 78%, 93%, 92%, and 80%, respectively. If, instead of severe CFR impairment, moderate impairment of CFR (2.5) was considered as a marker of restenosis, then sensitivity increased to 94%, with only a modest reduction in specificity (87%).
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Figure 3 Bar graph indicating coronary flow reserve (CFR) values for angiographic studies showing or not showing post-percutaneous transluminal coronary angioplasty restenosis (groups A and B). The mean values ± SD are also shown. LAD = left anterior descending coronary artery.
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Clinical findings and angiographic and coronary flow results.
Coronary angiography was performed before the established follow-up end in 16 patients: in 15 because of new clinical signs of angina (9 of these patients had LAD restenosis; 8 of these had an abnormal CFR, whereas the remaining patient had a normal CFR value, although in the low range [2.2]; in 6 of these patients, a new PTCA was performed; 1 patient was submitted to CABG, while the remaining 2 refused a new PTCA. Of the other 6 patients, all had normal CFR, without coronary restenosis). In the remaining patient, earlier coronary angiography was performed because an abnormal exercise stress test was found at four-month follow-up along with a reduction of CFR (1.06) and coronary restenosis of 61% at quantitative coronary angiography, but with no sign of angina. Among the 47 patients submitted to angiography at the scheduled end of the follow-up protocol, CFR was normal in 27 and abnormal in 20. Twenty-one of the 27 patients with normal CFR showed no significant restenosis at coronary angiography; 8 of these 27 patients had angina. Among the 20 patients with impaired CFR at the end of the scheduled follow-up, 18 had significant coronary restenosis (15 of these 18 patients had angina).
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Discussion
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This study demonstrates that noninvasive CFR assessment, obtained by means of CE-TTE, is an extremely feasible and highly accurate tool for detection of LAD restenosis after PTCA.
The use of PTCA as treatment of significant hemodynamic coronary stenosis has consistently increased over the past years. Treatment of LAD stenosis by PTCA is of particular clinical relevance, because its presence is an important independent risk factor of death, with an increased mortality rate at three years (15). However, coronary restenosis can develop early after PTCA (3), with an incidence varying from 12% to 60%, according to different series of patients (2,16,17). Most cases of restenosis usually occur within six months of PTCA (17), and about one-third of these develop in the absence of chest pain (18,19). Thus, clinical symptoms are considered inaccurate predictors of restenosis. Furthermore, coronary flow monitoring after PTCA is of particular clinical relevance in a specific subset of patients—for example, in diabetics in whom restenosis, as recently demonstrated, is a major determinant of long-term mortality (20). Because of the relevant incidence of LAD disease (21) and its important clinical impact, as well as the recurrent risk of restenosis after PTCA, a noninvasive, easily performable, and very accurate method capable of identifying LAD restenosis after PTCA could be extremely important from the clinical point of view.
Currently used diagnostic techniques have relatively limited diagnostic potential in this context, because they only provide indirect signs of restenosis. In fact, noninvasive diagnostic tests commonly used in the follow-up of patients submitted to PTCA, such as exercise stress electrocardiography (22), stress echocardiography (23) and nuclear perfusion studies (24), have a relatively poor sensitivity and low predictive value, especially in patients with single-vessel disease (25).
Doppler assessment of coronary restenosis after PTCA.
Contrast-enhanced transthoracic echocardiography is a new, feasible, and reliable tool for noninvasive measurement of CFR (9–12,26–28).
In previous reports from other laboratories (12,26–28), as well as from our own (9–11), feasibility ranged from 78% to 100% and was higher when contrast enhancement was employed (9–11). Hozumi et al. (12) and Caiati et al. (11) have shown that agreement between CE-TTE–derived and DFW-derived CFR was close, with an excellent correlation between invasive and noninvasive methods. Diagnostic accuracy of CE-TTE is comparable to that observed using much more expensive tools for CFR assessment, such as phase-contrast MRI (8). Our study has shown that CE-TTE appears to have great potential usefulness in the clinical follow-up of patients submitted to PTCA of the LAD, because of its noninvasiveness and therefore, easy repeatability. In our series of patients, some false-positive and false-negative studies occurred, as in other studies in which CFR was used for the same purpose (7,8). These discrepancies (limited in our study to 9 of our 63 CE-TTE angiographic comparisons: 7 false-positive and 2 false-negative) can be easily explained by the well-known limited relationship existing between functional and anatomic estimates of stenosis severity (4), especially when intermediate-severity restenosis is present (29), as found in most of this group of patients (Table 1).
Advantages of CE-TTE–derived CFR assessment in PTCA-treated follow-up patients.
The importance of CFR in assessing short- and long-term outcomes in a clinical follow-up of patients after PTCA has already been stressed by the Doppler Endpoints Balloon Angioplasty Trial Europe (DEBATE) study (30). This study assessed the predictive value of early post-PTCA CFR assessment with respect to the clinical outcome. In the DEBATE series of patients, a CFR value of >2.5, with a residual percent diameter stenosis <35%, was considered the best indicator of a low incidence of recurrence of symptoms at one- and six-month follow-up; however, the predictive values of this combined variable to detect restenosis were modest (10% vs. 19% and 23% vs. 47%, respectively). A possible explanation for this poor predictive power is that measurements were performed immediately after PTCA, when the CFR value can be temporarily impaired because of transient microcirculatory dysfunction. This temporary, reversible dysfunction can be explained by several possible mechanisms: release of microemboli (31), neurally mediated vasoconstriction (32) or microcirculatory vasospasm (33). Thus, the early CFR measurements, along with the impossibility of serially repeating CFR measurements, because of the invasiveness of the DFW procedure, could account for the low predictive value of DFW in the long-term follow-up of DEBATE patients. Because it is noninvasive and easily repeatable, CE-TTE allows serial CFR assessment not only soon after the PTCA procedure but also, more importantly, at a temporal distance from it, when the restoration of microvascular function allows a CFR estimate that is more closely related to the epicardial vessel’s anatomic condition.
Study limitations.
This method has several limitations. First of all, at present, CE-TTE–derived CFR evaluation can only be achieved in the LAD, leaving the circumflex and right coronary artery territories not suitable for CE-TTE study. Second, CFR assessment can be invalidated if measurements are performed at the coronary stenosis site (13) or if the LAD is totally occluded and flow in the LAD branches is falsely considered as flow in the main coronary artery. However, accurate LAD mapping and preliminary knowledge of the patient’s previous coronary anatomy, which are possible in this particular clinical context, can circumvent these limitations. Third, in this study, contrast enhancement was used for improving the feasibility of coronary flow recording. Nevertheless, as reported by other groups (12,28), adequate recording of LAD coronary flow and flow reserve can be successfully achieved, although with a lower feasibility and in the absence of concomitant infusion of a contrast agent. Finally, because the aim of this study was not to compare the diagnostic accuracy of this new method with other diagnostic techniques, established diagnostic procedures during patient follow-up were not generally performed in all patients; instead, they were scheduled according to the clinical picture of the patient and on the referring physician’s request.
Conclusions.
Contrast-enhanced transthoracic evaluation of CFR in the LAD is a new, feasible, and accurate tool for the detection of significant LAD stenosis, as well as for the identification of post-PTCA LAD restenosis. The results of this study confirm and extend previous data reported from our group on the diagnostic potential of this new approach (9–11). To investigate, in more depth, this diagnostic tool’s potential and to compare it with established diagnostic procedures, larger studies are needed. These future studies should be aimed at detecting the diagnostic potential in a larger population, as well at defining the long-term clinical impact of noninvasively detected post-PTCA restenosis in the absence of clinical signs of ischemia.
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Acknowledgments
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The authors thank Andrea Puddu, Medical Technician, and Maria Domenica Gaias, RN, for their technical support; Mrs. Barbara Hildenbrand for her assistance in the preparation of this manuscript; and Otto M. Hess, MD (University of Berna, Switzerland), Thomas F. Lüscher, MD, and Zhihong Hiang, PhD (University of Zurich, Switzerland) for their precious support in quantitative angiographic measurements.
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Abstract
Methods